Vehicle powertrains may include transmissions to transfer power and torque from an engine to the vehicle output (axles or wheels). Hybrid powertrains may include multiple primary movers, including internal combustion engines or alternative power sources, such as one or more electric machines coupled with an energy storage device. When the powertrain is equipped with an additional primary mover, such as an electric machine, the transmission may also transfer torque and power from the electric machine to provide traction for the vehicle. Fixed-gears or speed ratios allow the engine to operate within a narrow range of speeds while providing a wide range of output speeds to the powertrain.
Vehicles having either conventional internal combustion or hybrid gasoline/electric transmissions typically utilize a torque-transmitting device know as a clutch or clutch pack for smoothly engaging or coupling two rotating bodies or shafts to transmit torque therebetween. Likewise, the same clutch or clutch pack is used to subsequently disengage the coupled shafts to interrupt the power transfer and permit, for example, a smooth shifting between the various gears of a gear set and/or decoupling of one or more motor/generators.
One or more of the clutches in a vehicle may be configured as a wet clutch which may be used, for example, in an automatic transmission, a Dual Clutch Transmission (DCT), a transfer case or a fan drive of the vehicle. One or more of the clutches in a vehicle may be configured as a dry clutch which may be used, for example, in a dry DCT or an automated manual transmission. Engagement and disengagement of each of these clutches or clutch packs may occur through control of hydraulic valves linked to hydraulic components. The hydraulic pressure regulated or provided by these valves actuates the clutch engagement and disengagement.